chai-defendernpm
chai-defender is a confirmed malicious npm package (MAL-2026-10050) that typosquats a legitimate package to trick installs (malicious versions 1.0.0-beta.1, 1.0.1, 1.0.1-beta…). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in chai-defender (npm)
What this malware does
On require('chai-defender'), index.js invokes launchDeflectBootstrap() which spawns a detached background node process running lib/caller.js. That process loads lib/initstate.js, which performs an HTTP GET against a hardcoded remote endpoint (http://check-server-state.vercel.app/server/v2) and passes the response body into new Function('require', <response>)(require), executing attacker-controlled JavaScript with access to Node's require in the installer's process. The package presents itself as a Chai assertions plugin ('Security-focused Chai assertions'), but this fetch-and-exec behavior is unrelated to any assertion functionality. The lib/ directory is padded with files whose names mimic the pino logger project (multistream.js, transport.js, redaction.js, levels.js, symbols.js, worker.js) and reference a non-existent./flowlimit.js module; these files are not wired into index.js and appear to exist to make the package look substantial while the real payload is lib/const.js + lib/initstate.js. Plain HTTP transport additionally exposes the eval channel to in-path payload injection. Any project that requires this package hands remote code execution to whoever controls check-server-state.vercel.app.
Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
TyposquatFind it
Scan your lockfiles (package-lock.json, pnpm-lock.yaml, yarn.lock, requirements.txt, poetry.lock, etc.) and build artifacts for chai-defender (6 malicious versions). O3 Security's supply-chain scanner checks every dependency against known-malicious package intelligence at install time and in CI, flagging chai-defender across your stack and pipelines.
If you installed it — respond
chai-defender is a typosquat — you almost certainly intended a legitimately-named package. Remove chai-defender, install the correct package, and rotate any secrets exposed during the install since post-install scripts may have already run.
Did it already run?
If chai-defender was ever installed, its post-install/runtime payload may have already executed. O3's L7 egress monitoring and runtime eBPF sensors detect the credential exfiltration or command-and-control callback after install and block the malicious outbound channel, so you catch and contain the actual compromise — not just the presence of the package.
How O3 protects you
O3 blocks chai-defender before install through its supply-chain scanner, and if it has already run, detects and severs the exfiltration or C2 callback at runtime through L7 egress monitoring and eBPF.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
Detect & block this
O3 blocks chai-defender-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.